In my fairly uninformed opinion, power conditioners are of use when the power fluctuates and you get spikes in the supply voltage--that sorta thing.
That's a regulator. They're designed to smooth out power fluctuations and whatnot, and some have an internal battery to deal with sags.
A power conditioner is used to filter excess noise from the mains (wall)power supply. If you want to see what a noisy power supply can do, go turn on your vaccuum cleaner while watching the TV. You can get the same sort of noise from many electric motors, including the motors for refridgerators and freezers, as well as the ballasts found in flourescent lighting.
A good way to test to see if the hum is from the mains power is to unplug your guitar, lead, and remove anything from the FX loop. Since you just removed most other sources of noise (pickups, poorly shielded guitar, poorly sheilded cables) if it still buzzes, there's a good chance it's from the power.
I use a Furman PL Plus....I believe the only difference between it and the PL-8 is slight difference in quality. The PL-Pro is more than what you need, and and requires a special plug. If you're in the UK make sure you get one with the "E" designation (PL-8E), since it's designed for use with 220-240v, 50hz. I believe they also make some smaller conditioners that aren't rackmounted, such as the Power Factor unit. I have no experience with these, but I believe they're basically the same unit mounted in a different chassis.